1. Field of Invention
The present invention relates to an enclosure for avoiding leakage of fluid into the ground environment with emphasis upon hydraulic elevator fluid containment. Further the invention allows a positive test to insure continuing containment.
2. Background
Current increased awareness recognizes that an underground system containing hazardous fluids can become an environmental problem if the system leaks. Much emphasis has been expended to design systems to dispense gasoline from underground tanks in response to the Federal Environmental Protection Agency as well as many state laws and regulations. Other hazardous fluids are also receiving increased attention.
A particular situation involving a hazardous fluid is the fluid utilized in hydraulic ram elevators. Hydraulic elevators have been employed from many decades and one of the most successful of its early uses was to provide lift for aircraft carriers between the flight deck and the aircraft storage and maintenance levels.
Because such elevators in commercial applications must extend upward several floors, the hydraulic ram cylinder is buried a similar distance underground creating a potential environmental problem, especially to ground water, if the cylinder develops fluid leaks.
With the hydraulic ram system, such ram rides in a cylinder and is moved by hydraulic fluid pressure of up to design conditions of 650 psi; however, actual operating pressures more normally range up to about 450 psi. Any missalignment of the ram and its cylinder can result in sufficient friction over time resulting in the possible wearing through of the cylinder wall and fluid leakage underground. The repair of such a breached cylinder often results in pulling of the whole elevator assembly which is very expensive particularly if the roof of the building is breached to allow large crane access. Of course the hydraulic seals, piping, valves and pump can all obtain leaks over time, but these are well positioned for monitoring and repair.
Because of the design of hydraulic elevators secondary containment systems are only located outside of the cylinder; inner linings used as containment, if they are at all feasible, are difficult to install and maintain.
Corrosion problems are a very big, and expensive, aspect of hydraulic elevators. With much ground water normally in contact with the hydraulic ram outer cylinder, electrolytic corrosion often eats through this cylinder wall, especially since these elevators are expected to last the life of the building, which is likely 50 or more years. Thus hydraulic fluid leakage in old elevators is common.
When working underground it is common to line pipe trenches with a flexible membrane to attempt to contain leakage. This attempt makes it difficult to monitor integrity as well as requiring separate installation steps. It is not a useful approach with hydraulic elevators that require containment integrity measurements and are typically installed in one piece because of water flooding of the drilled hole.
Related United States patents that disclose containment ideas include:
______________________________________ U.S. Pat. No. Year Inventor ______________________________________ 4,462,249 1984 Adams 4,796,676 1989 Hendershot et al 4,971,477 1990 Webb-1 et al 5,098,221 1992 Osborne 5,263,794 1993 Webb-2 5,297,896 1994 Webb-3 ______________________________________
Referring to the above list, Adams discloses a tank leakage detection method where leakage perforates the tank allowing air outside the tank to leak in when the tank's own pressure is lowered and in so doing forms air bubbles that are acoustically detected. A special acoustical detector is required as well as equipment for creating a vacuum on said tank.
Hendershot et al disclose a fluid storage tank system containing a rigid external primary tank with flexible secondary inner-lining. Negative pressure formed by a vacuum between them is monitored and decreases if fluid leaks. The tank has a difficult to install inner-lining and requires vacuum conditions.
Webb-1 et al disclose a secondary contained fluid supply system having two chambers connected with pipe using a second flexible inner pipe that is removable by access through a chamber. The containment is a double pipe arrangement but monitoring is difficult unless the flexible pipe is removed. This is designed to move liquids such as gasoline from underground tanks to an above-ground dispenser.
Osborne discloses a flexible double-containment piping system for underground storage tanks using double pipe containment having quick-disconnect coupling. This system is designed primarily for gasoline tanks using an above-ground dispenser.
Webb-2 discloses an environmentally safe underground piping system having an outer rigid pipe with flexible inner tube to carry fluid. Accent is on quick connections. This is an improvement on Webb-1 et al and is designed to move liquids such as gasoline from underground tanks to an above-ground dispenser.
Webb-3 discloses environmentally safe underground piping system using a double-walled pipe with gravity flow of leaking fluid through the outer pipe back to the storage tank. Sump pit detects leakage. This is an improvement to Webb-2 and is designed to move liquids such as gasoline from underground tanks to an above-ground dispenser.